Earth's atmosphere is a layer of gases that surround it, permitting life and protecting life by absorbing ultraviolet solar radiation, warming the surface by retaining the heat and mitigating the temperature difference between day and night.

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74
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11answers
10k views

Why is filling a balloon from your mouth much harder initially?

Why is it that when you first fill up a balloon, it's hard to get air through, but after inflating it a bit, it becomes much easier to further inflate the balloon?
3
votes
3answers
223 views

Why $e$ in the formula for air density?

I am reading a book that says that the density of air is approximately $D = 1.25 e^{(-0.0001h)}$, where h is the height in meters. Why is Euler's number $e$ used here? Was a differential equation ...
1
vote
0answers
88 views

What kinds of reactions happen when bubbling air through water?

Mostly I have seen air bubbling used to remove impurities in the water itself, like exemplified in this course packet. This is called "Sparging," but I have yet to learn much about transfer between ...
1
vote
0answers
49 views

Cost vs. purity producing liquid oxygen [closed]

We are a group of rocket amatures who build rockets using LOX and ethanol as propellent. We normally buy the LOX from supplier. But lately we have been discussing if there is an easy way to produce it ...
3
votes
2answers
360 views

How is a vacuum formed and measured by this pneumatics attachment?

Please excuse me if this question is misplaced and also for my narrow understanding of physics. Firstly, I'm asking simply because the robot I've now been set to work with uses an air pneumatics ...
25
votes
5answers
9k views

Why do heavier objects fall faster in air?

We all know that in an idealised world all objects accelerate at the same rate when dropped regardless of their mass. We also know that in reality (or more accurately, in air) a lead feather falls ...
4
votes
3answers
327 views

Make air reflect light

Is there any way in which air can be made to reflect light? By making air denser or by any other way? The task is to project images in air...
0
votes
0answers
40 views

Help with vacuums?

Okay, here is my understanding. Please correct me if anything here is incorrect. Suppose I have a cube with a side length of ten inches. It has a surface area of 600 square inches, and at an ...
2
votes
1answer
138 views

Which air will give more effective cooling ? Dry or Moist?

Yesterday, I had an innovative idea. I live in India, and in summer season, the temperature can reach up to 45 degree Celsius. We use Split 1.5 Ton AC in our small office. The idea is to put an ...
3
votes
2answers
145 views

Why is a material such as plastic air-tight?

I'm not too familiar with fluid mechanics, but i always wondered how let's say plastic containers would be able to contain a fluid, such as gas or water. How does plastic prevent the molecules of the ...
1
vote
2answers
525 views

Balloon, lighter than air and vacuum?

As I understand, in a balloon/air balloon, a gas burner is used to heat air or using some lighter atom like helium. Since helium or hot air is lighter and less dense than the cool air around the ...
0
votes
1answer
32 views

Can low end hepa vaccums still clean near all of the air?

In the US HEPA filters will remove 99.97% of particles sized 0.3 microns. In Europe HEPA filters do not have to meet this exact figure and there are different classes of HEPA filters e.g. h10(removes ...
2
votes
1answer
183 views

Can a vacuum cleaner be used to purify the air in a small room? [closed]

A hepa vacuum cleaner will pick up fine dust from the floor, filter it and send the clean air out through the exhaust. However with movement in the room fine dust will also be goinng up in the air ...
33
votes
9answers
9k views

Why can't we see gases?

I am not sure what causes gas molecules to be invisible.This question may look silly but I really want to know the story behind it.
2
votes
1answer
267 views

How to calculate differential pressure

A ventilator fan mounted on the wall of an air tight room(except for an air intake with a given cross sectional area) is blowing air out of the room. If air displacement rate of the fan is given(CFM ...
5
votes
3answers
234 views

What is the difference between a puff of air and a sound wave regarding creation and propagation?

While watching a Schlieren video of a hand clapping, I noted a very distinct difference between a sound wave and a puff of air, which were both created by a hand clapping. What is the difference ...
0
votes
2answers
96 views

Why does my eardrum feel strange inside a car?

When I was riding a car (I was not the driver), my eardrum felt a little similar to the case when I was in a plane that was taking off, and little loss of hearing. Nothing was played inside. The ...
0
votes
1answer
38 views

Change in volume of air held at the top of a tube with upper end closed and holding some liquid [closed]

Consider a tube both end open.dip one end in a container with water..close the top with your thumb..(make sure some air remains between your thumb and the liquid in the tube)..now take the tube out of ...
1
vote
1answer
103 views

Pressure at the front and back of a fan

I have a fan which is inside a duct. When the fan is off, the pressure at the front and back of the blade remains the same. Now when it is running, the velocity of the air below will be more because ...
15
votes
5answers
4k views

Why isn't jumping from a high altitude fatal?

After seeing this answer claiming that displacing matter "In a very short time", "no matter whether the matter is solid, liquid, or gas" (even though he concludes that falling from a high altitude is ...
2
votes
3answers
419 views

Would we be able to hear the sun if space were full of air? [duplicate]

I was wondering if the sun could be audible from earth in an air-filled space scenario. We can ignore all the other disastrous consequences! Thanks!
2
votes
1answer
456 views

Vortex Air Intake

Why is a vortex air intake in an engine cause the fuel to burn more efficiently within a vehicle. Why is this more efficient.
1
vote
1answer
266 views

A bomb can be made to explode or implode? [closed]

A bomb can be made to implode or explode. Can one be made to explode while creating a vortex at the same time?
31
votes
6answers
18k views

Why is jumping into water from high altitude fatal?

If I jump from an airplane straight positioned upright into the ocean, why is it the same as jumping straight on the ground? Water is a liquid as opposed to the ground, so I would expect that by ...
2
votes
2answers
667 views

Beryllium Vacuum Sphere Boat/Aircraft

Is it possible to make a solid rigid evacuated "balloon" out of Beryllium or other elements or alloys? The critical buckling pressure at which an evacuated sphere is given as $$ ...
0
votes
1answer
105 views

Viability of Dysons bladeless fans? [closed]

Do Dyson's bladeless fans produce enough air pressure to cool say an air conditioning unit and do they produce a vortex pressure like a bladed fan?
0
votes
2answers
6k views

Why do particles in high pressure air always flow to lower pressure?

The title really says it all: Why is this case? A "Feynman type" answer would be really appreciated as I'm more of a layman that a physicist.
1
vote
3answers
1k views

How could electromagnetic waves propagate through space although they have no electrons?

How could electric fields in these waves propagate through space although in space there's no electrons for the electric field to be formed? is there another type of charged particles that carry the ...
3
votes
2answers
61 views

Does Coriolis effect affect snowing?

Right now, outside is snowing. No matter what window I look from, the snow constantly for last few hours tends to fall to the right close to the window, and to the left close to the building across ...
0
votes
2answers
189 views

Small object in air

What happens with very small spherical objects ($d=1\mu m$, e.g. a bacterium) in air? Do they fall? How quickly? Does it depend on their mass? We often see objects of little mass e.g. leaves falling ...
1
vote
3answers
2k views

What makes water heavier than air?

I apologize in advance if this is too basic for this site. Considering that hydrogen is lighter then oxygen, and water is 2/3 hydrogen, and only 1/3 oxygen, and our "air" is comprised mainly of ...
3
votes
1answer
63 views

Why would air try to escape from under a pot?

I put a wet Calphalon pot down flat on a wet synthetic countertop. None of the surfaces or liquids was hot. Bubbles started appearing a second or two later from under the rim of the pot in one area. ...
0
votes
1answer
2k views

Which one conducts heat better: water, or air?

If we were to assume room temperature of 20C, which of the fluids conducts heat better, and why?
0
votes
1answer
2k views

HEPA vs. water filter in vacuum cleaning [closed]

What is the difference between air being filtered with HEPA or water? Which one performs better within a non-allergic home environment? Does water filter have a meaning still when common vacuum ...
11
votes
5answers
6k views

Why does my door shut faster when the window is open?

I've noticed that if I shut my door when the window is open in a room, the door will tend to shut faster. If I shut the door when the window is closed with a normal force it will not fully close as if ...
0
votes
2answers
133 views

Simulate free fall in a rotating torus?

Say I have a rotating torus filled with air at 1 atmospheric pressure at sufficient speed (and inclined along the direction of the force of gravity with respect to Earth). If the rotation speed were ...
3
votes
2answers
702 views

Why did they used to make the mill chimneys so tall?

Why did they used to make the mill chimneys so tall? This question was asked in an Engineering Interview at Cambridge University.
30
votes
7answers
5k views

Is it possible to “cook” pasta at room temperature with low enough pressure?

It is known fact, that boiling point of water decreases by decreasing of pressure. So there is a pressure at which water boils at room temperature. Would it be possible to cook e.g. pasta at room ...
1
vote
1answer
101 views

Velocity in the lift equation

What exactly is the nature of the velocity in the lift equation? I have read that it is the velocity of the aircraft, and I think I have read that it is the relative velocity of the air to the ...
0
votes
2answers
82 views

What will happen to a compressible fluid filled inside a sealed container when the container begins to accelerate?

Assume the fluid to be air and the container to be a car, will there be a pressure gradient which will result the fluid to stack at one end of the car or there is something else that I'm missing?
1
vote
1answer
329 views

How does air escape from a pneumatic tire?

Obviously, it is caused by the difference in pressure between the inside of the tire and its surrounding environment; but how specifically is the air escaping?
2
votes
1answer
142 views

Whirlwind/tornado/dust devil in the middle of nowhere

I live in area which have many properties similar to desert. Many times when I drive by I see a whirlwind/tornado/dust devil of sand or other garbage parts. I would like to ask how this was normally ...
4
votes
4answers
3k views

Dyson Air Blade as a propulsion system?

I've read from many sources that Dyson Air Multipliers are more efficient and quieter than normal fans. Now, with the proof of concept, is it possible to use its principles as a propulsion system for, ...
0
votes
2answers
289 views

Weighing a flying bird [duplicate]

Let thing of a bird standing still in a box on top of a weighing machine that shows a mass $m_0$. Now, imagine that the bird is flying, still in the same box and the same weighing machine shows a mass ...
3
votes
1answer
621 views

How to Calculate temperature, given speed of sound and relative humidity?

I know the solution in reverse direction, but I find it very complex to go the other way around and calculate the temperature when given the speed of sound and relative humidity, any ideas?
1
vote
1answer
338 views

Drag/air-resistance impulse

I'm simulating snowfall in a discrete-time physics engine, using this formula for the drag force on a snowflake: $F_d=CAv^2$ (where $A$ is the flake's cross-sectional area and $C$ is a catch-all ...
5
votes
2answers
614 views

How can you calculate air resistances at different speeds?

I've read that at 50mph air resistance to an average car is the equivalent of driving through water and at 80mph it's the equivalent of driving through oil. I can't find any references online to ...
7
votes
3answers
129 views

Reason for strange “canyons” of dust on the cooling platform

I took apart my cooling platform Something like this : And I found something like this inside : I wonder why around the hollows are the "canyon like" structures. PS: I also drop this platform ...
1
vote
0answers
60 views

Closed pipe/sound resonance sound type sound coming from mineral processing plant

I work near a very large mineral processing plant which does vibrate our building and there is also a sound/feeling very similar to the closed pipe/sound resonance that is achieved when opening a back ...
3
votes
1answer
408 views

Static pressure of free air stream

One of the common misunderstandings regarding Bernoulli's principle is that, in general, "faster moving air has lower pressure". Bernoulli's principle can only be applied to asingle streamline in ...